Enhancing color stability to sterilizing radiation of polymer compositions

ABSTRACT

Compounds having defined functional groups are described which color stabilize aromatic carbonate polymers or blends therewith upon exposure to steriliizing radiation.

This is a continuation of co-pending application Ser. No. 07/136,602,filed on Dec. 22, 1987, now U.S. Pat. No. 4,880,856, which is adivisional of application Ser. No. 769,277, filed on Aug. 26, 1985,abandoned, which is a continuation-in-part of application Ser. No. 579,103, filed Feb. 10, 1984, abandoned.

This invention relates to aromatic carbonate polymers and blendscontaining carbonate polymers rendered resistant to yellowing bysterilizing irradiation. More particularly, this invention relates toaromatic carbonate polymers containing certain additives havingfunctional groups effective to color stabilize such polymers uponexposure to sterilizing radiation.

BACKGROUND OF THE INVENTION

Aromatic carbonate polymers are well known thermoplastic materialswhich, due to their many advantageous properties, find use asthermoplastic engineering materials. The aromatic carbonate polymersexhibit, for example, excellent properties of toughness, impactresistance, heat resistance and dimensional stability. Not only aremolded parts prepared from aromatic carbonate polymers, but films andsheet materials as well. Because of its excellent property spectrum,aromatic carbonate polymers such as aromatic polycarbonate have beenproposed for various utilities including those relating to medicalpackaging, for example the containers in which syringes, surgicalinstruments, intravenous fluids, operating room devices, and the likeare maintained. Additionally polycarbonate has been used in medicaldevices such as blood oxygenators, anesthesia canisters, intravenousconnectors and accessories, blood centrifuge bowls, surgical instrumentsand operating room instruments. The toughness of the polycarbonate aswell as its clarity, high heat resistance, strength and good bloodcompatibility make it a potential substance of choice in this hightechnology medical device and packaging market. Sterilization of thesearticles used in the medical arts and other technologies is often timesrequired.

However, one particular difficulty with certain sterilization techniqueshas been discovered. A typical method of sterilizing various objectsuseful in medical practice is through irradiation. The type of radiationusually employed is low level gamma or electron beam radiation. It isreadily apparent that the level of such radiation which accomplishes thesterilization is significantly above that of ordinary backgroundradiation. When exposed to radiation which is of sufficient strength andduration to sterilize various objects, the aromatic carbonate polymericmaterial is subject to yellowing. This yellowing of the aromaticcarbonate reduces its clarity and alters its appearance and therebyreduces its utility. Not only packaging materials such as flexiblearomatic carbonate film and sheet products but also molded parts as wellsuffer from this yellowing phenomonon.

New additives have been discovered which inhibit the yellowing ofaromatic carbonate polymers after exposure to sterilization irradiation.Thus, particularly in the medical and food industries, the utility ofpolycarbonate film, sheet, and molded parts may be increased.

DESCRIPTION OF THE INVENTION

Briefly, according to the present invention, there are providedsterilizing radiation color stabilized aromatic carbonate polymers whichcontain an effective amount of a stabilizing compound effective toinhibit yellowing upon sterilizing radiation exposure, the compound isselected from the group consisting of organic acids (--COOH), esters(--COOR³), alcohols (--OH), thiols, thioethers and cyclic thioethers,anilides (--NHC₆ H₅), amines (--NH₂), oxamides (NHCOCONH₂), diketones(>CO), sulfones (--SO₂ --), alkenes (>C=C<), hydroaromatics, and pyranylcompounds.

Aromatic carbonate polymer generally includes both the polycarbonatesand the copolyestercarbonates. The aromatic polycarbonate resins for useherein can be prepared by reacting a dihydric phenol with a carbonateprecursor, such as phosgene, a haloformate or a carbonate ester.Generally speaking, such carbonate polymers may be typified aspossessing recurring structural units of the formula: ##STR1## wherein Ais a divalent aromatic radical of the dihydric phenol employed in thepolymer producing reaction. Preferably, the carbonate polymers used toprovide the resinous mixtures of the invention have an intrinsicviscosity (as measured in methylene chloride at 25° C.) ranging fromabout 0.30 to about 1.00 dl/g. The dihydric phenols which may beemployed to provide such aromatic carbonate polymers are mononuclear orpolynuclear aromatic compounds, containing as functional groups twohydroxy radicals, each of which is attached directly to a carbon atom ofan aromatic nucleus. Typical dihydric phenols are:

2,2-bis(4-hydroxyphenyl)propane;

hydroquinone;

resorcinol;

2,2-bis-(4-hydroxyphenyl)pentane;

2,4'-dihydroxydiphenylmethane;

bis-(2-hydroxyphenyl)methane;

bis-(4-hydroxyphenyl)methane;

bis-(4-hydroxy-5-nitrophenyl)methane;

1.1,-bis(4-hydroxyphenyl)ethane;

3,3-bis(4-hydroxyphenyl)pentane;

2,2-dihydroxydiphenyl;

2,6-dihydroxynaphthalene;

bis-(4-hydroxydiphenyl)sulfone;

bis-(3,5-diethyl-4-hydroxyphenyl)sulfone;

2,2-bis-(3,5-dimethyl-4-hydroxyphenyl)propane;

2,4'-dihydroxydiphenyl sulfone;

5'-chloro-2,4'-dihydroxydiphenyl sulfone;

bis-(4-hydroxyphenyl)diphenyl sulfone;

4,4'-dihydroxydiphenyl ether;

4,4'-dihydroxy-3,3'-dichlorodiphenyl ether;

4,4'-dihydroxy-2,5-dihydroxydiphenyl ether; and the like.

Other dihydric phenols which are also suitable for use in thepreparation of the above polycarbonates are disclosed in U.S. Pat. No.2,999,835; 3,028,365; 3,334,154; and 4,131,575.

These aromatic polycarbonates can be manufactured by known processes,such as, for example and as mentioned above, by reacting a dihydricphenol with a carbonate precursor, such as phosgene, in accordance withmethods set forth in the above-cited literature and U.S. Pat. No.4,018,750 and 4,123,436, or by transesterification processes such as aredisclosed in U.S. Pat. No. 3,153,008, as well as other processes knownto those skilled in the art.

It is possible to employ two or more different dihydric phenols or acopolymer of a dihydric phenol with a glycol or with a hydroxy or acidterminated polyester or with a dibasic acid in the event a carbonatecopolymer or interpolymer rather than a homopolymer is desired for usein the preparation of the polycarbonate mixtures of the invention.Branched polycarbonates are also useful, such as are described in U.S.Pat. No. 4,001,184, also there can be utilized blends of a linearpolycarbonate and a branched polycarbonate. Moreover, blends of any ofthe above materials may be employed in the practice of this invention toprovide the aromatic polycarbonate. In any event, the preferred aromaticcarbonate polymer for use as component (a) (i) herein is a homopolymerderived from 2,2-bis(4-hydroxyphenyl)propane (bisphenol-A).

The copolyestercarbonate usually employed may generally be described aspolymers comprising recurring carbonate groups, ##STR2## carboxylategroups, ##STR3## and aromatic carboxylic groups in the linear polymerchain, in which at least some of the carboxylate groups and at leastsome of the carbonate groups are bonded directly to ring carbon atoms ofthe aromatic carboxylic groups. These copolyestercarbonate copolymers ingeneral, are prepared by reacting a difunctional carboxylic acid orester forming derivative, a dihydric phenol and a carbonate precursor.

The dihydric phenols useful in formulating the copolyestercarbonates foruse herein may be represented by the general formula: ##STR4## in whichA is an aromatic group such as phenylene, biphenylene, naphthylene,anthrylene, etc. E may be an alkylene or alkylidene group such asmethylene, ethylene, propylene, propylidene, isopropylidene, butylene,butylidene, isobutylidene, amylene, isoamylene, amylidene, isoamylidineand generally from one to twelve carbon atoms, inclusive, etc. Where Eis an alkylene or alkylidene group, it may also consist of two or morealkylene or alkylidene groups, connected by a nonalkylene ornon-alkylidene group such as an aromatic linkage, a tertiary aminolinkage, an ether linkage, a carbonyl linkage, a silicon-containinglinkage, or by a sulfur-containing linkage such as sulfide, sulfoxide,sulfone, etc. In addition, E may be a cycloaliphatic group of five toseven carbon atoms, inclusive (e.g. cyclopentyl, cyclohexyl), or acycloalkylidene of five to seven carbon atoms inclusive, such ascyclohexylidene, a sulfur containing linkage, such as sulfide, sulfoxideor sulfone; an ether linkage; a carbonyl group; a tertiary nitrogengroup, or a silicon containing linkage such as silane or siloxy. Othergroups which E may represent will occur to those skilled in the art. Ris hydrogen or a monovalent hydrocarbon group such as alkyl of one toeight carbon atoms, inclusive (methyl, ethyl, propyl, etc.), aryl(phenyl, naphthyl, etc.), aralkyl (benzyl, ethylphenyl, etc.) orcycloaliphatic of five to seven carbon atoms, inclusive (cyclopentyl,cyclohexyl, etc.). Y may be an inorganic atom such as chlorine, bromine,fluorine, etc.; an organic group such as the nitro group, etc.; anorganic group such as R above, or an oxy group such as OR, it being onlynecessary that Y h=inert to and unaffected by the reactants and thereaction conditions. The letter m is any whole number from and includingzero through the number of positions on A available for substitution; pis any whole number from and including zero through the number ofavailable positions on E; t is a whole number equal to at least one, Sis either zero or one, and u is any whole number including zero.

In the dihydric phenol compound represented by Formula II above, whenmore than one Y substituent is present, they may be the same ordifferent. The same is true for the R substituent. Where s is zero inFormula II and u is not zero, the aromatic rings are directly joinedwith no intervening alkylene or other bridge. The positions of thehydroxyl groups and Y on the aromatic nuclear residues A can be variedin the ortho, meta, or para positions and the groupings can be in avicinal, asymmetrical or symmetrical relationship, where two or morering carbon atoms of the aromatic hydrocarbon residue are substitutedwith Y and hydroxyl group.

Examples hydric phenol compounds that may be employed in thecopolyestercarbonate include:

2,2-bis-(4-hydroxyphenyl)propane(bisphenol-A);

2,4'-dihydroxydiphenylmethane;

bis-(2-hydroxyphenyl)methane;

bis-(4-hydroxyphenyl)methane;

bis-(4-hydroxy-5-nitrophenyl)methane;

bis-(4-hydroxy-2,6-dimethyl-3-methoxyphenyl)methane;

- 1,1-bis-(4-hydroxyphenyl)ethane;

1,2-bis-(4-hydroxyphenyl)ethane;

1,1-bis-(4-hydroxy-2-chlorophenyl)ethane;

1,1-bis-(2,5-dimethyl-4-hydroxyphenyl)ethane;

1,3-bis-(3-methyl-4-hydroxyphenyl)propane;

2,2-bis-(3-phenyl-4-hydroxyphenyl)propane;

2,2-bis-(3-isopropyl-4-hydroxyphenyl)propane;

2,2-bis-(4-hydroxynaphthyl)propane;

2,2-bis-(4-hydroxyphenyl)pentane;

3,3-bis-(4-hydroxyphenyl)pentane;

2,2-bis-(4-hydroxyphenyl)heptane;

bis-(4-hydroxyphenyl)phenylmethane;

bis-(4-hydroxyphenyl)cyclohexylmethane;

1,2-bis-(4-hydroxyphenyl)-1,2-bis-(phenyl)propane;

2,2-bis-(4-hydroxyphenyl)-1-phenylpropane; and the like. Also includedare dihydroxybenzenes typified by hydroquinone and resorcinol,dihydroxydiphenyls such as 4,4'-dihydroxydiphenyl;2,2'-dihydroxydiphenyl; 2,4'-dihydroxydiphenyl; dihydroxy-naphthalenessuch as 2,6-dihydroxynaphthalene, etc.

Also useful are dihydric phenols wherein E is a sulfur containingradical such as the dihydroxy aryl sulfones exemplified by:bis-(4-hydroxyphenyl)sulfone; 2,4'-dihydroxydiphenyl sulfone;5-chloro-2,4'-dihydroxy diphenyl sulfone; 3-chloro-bis-(4-hydroxyphenyl)sulfone; and 4,4'-dihydroxytriphenyldisulfone; etc. The preparation ofthese and other useful sulfones are described in U.S. Pat. No.2,288,282. Polysulfones as well as substituted sulfones using halogen,nitrogen, alkyl radicals, etc. are also useful.

Dihydroxy aromatic ethers such as those described in U.S. Pat. No.3,148,172 are useful as the dihydric phenol herein. The dihydroxyaromatic ethers may be prepared as described in U.S. Pat. No. 2,739,171.Illustrative of such compounds are the following:

4,4'-dihydroxydiphenyl ether;

4,4'-dihydroxytriphenyl ether;

the 4,3'-, 4,2'-, 4,1'-, 2,2'-, 2,3'-, etc. dihydroxydiphenyl ethers;

4,4'-dihydroxy-2,6-dimethyldiphenyl ether;

4,4'-dihydroxy-2,5-dimethyldiphenyl ether;

4,4'-dihydroxy-3,3'-diisobutyldiphenyl ether;

4,4'-dihydroxy-3,3'-diisopropyldiphenyl ether;

4,4'-dihydroxy-3,3'-dinitrodiphenyl ether;

4,4'-dihydroxy-3,3'-dichlorodiphenyl ether;

4,4'-dihydroxy-3,3'-dichlorodiphenyl ether;

4,4'-dihydroxy-2,3'-dibromodiphenyl ether;

4,4'-dihydroxydinaphthyl ether;

4,4'-dihydroxy-3,3'-dichlorodinaphthyl ether;

2,4-dihydroxytetraphenyl ether;

4,4'-dihydroxypentaphenyl ether;

4,4'-dihydroxy-2,6-dimethoxydiphenyl ether;

4,4'-dihydroxy-2,5-diethoxy-diphenyl ether, etc.

Mixtures of the dihydric phenols can also be employed and where dihydricphenol is mentioned herein, mixtures of such materials are considered tobe included.

In general, any difunctional carboxylic acid or its reactive derivativesuch as the acid halide conventionally used in the preparation ofpolyesters may be used for the preparation of polyestercarbonates usefulin formulating the compositions of the present invention. In general,the carboxylic acids which may be used include the aliphatic carboxylicacids, aliphatic aromatic carboxylic acids, or aromatic carboxylicacids. The aromatic dicarboxylic acids or their reactive derivativessuch as the aromatic diacid halides are preferred as they produce thearomatic polyestercarbonates which are most useful, from the standpointof physical properties, in the practice of the instant invention.

These carboxylic acids may be represented by the general formula:##STR5## wherein R¹ represents an alkylene, alkylidene or cycloaliphaticgroup in the same manner as set out above for E in Formula II; analkylene, alkylidene or cycloaliphatic group containing ethylenicunsaturation; an aromatic radical such as phenylene, naphthylene,bisphenylene, substituted phenylene, etc.; two or more aromatic groupsconnected through non-aromatic linkages such as those defined by E inFormula II; or a divalent aliphatic aromatic hydrocarbon radical such asan aralkyl or alkaryl radical. R² is either a carboxyl or a hydroxylgroup. The letter q represents the integer one where R² is a hydroxylgroup and either zero or one where R² is a carboxyl group. Thus thedifunctional carboxylic acid will either be a monohydroxy monocarboxylicacid or a dicarboxylic acid. For purposes of the present invention thearomatic dicarboxylic acids or their reactive derivatives such as, forexample, the acid halides, are preferred. Thus in these preferredaromatic dicarboxylic acids, as represented by Formula II, R² is acarboxyl group and R¹ is an aromatic radical such as phenylene,biphenylene, naphthylene, substituted phenylene, etc., two or morearomatic groups connected through non-aromatic linkages; or a divalentaliphatic aromatic radical. Some nonlimiting examples of suitablepreferred aromatic dicarboxylic acids which may be used in preparing thethe copolyestercarbonate resins of the instant invention includephthalic acid, isophthalic acid, terephthalic acid, homophthalic acid,o-, m-, and p-phenylenediacetic acid, the polynuclear aromatic acidssuch as diphenic acid, and 1,4-naphthalic acid. The aromatics may besubstituted with Y groups in the same manner as the formula I aromaticsare substituted.

These acids may be used individually or as mixtures of two or moredifferent acids.

The carbonate precursor may be either a carbonyl halide, a carbonateester, or a haloformate. The carbonyl halides which can be employedherein are carbonyl chlorides and carbonyl bromide. Typical of thecarbonate esters which may be employed herein are diphenyl carbonate,di(halophenyl)carbonates such as di(chlorophenyl)carbonate,di(bromophenyl)carbonate, di(trichlorophenyl)carbonate,di(tribromophenyl)carbonate, etc., di(alkylphenyl)carbonates such asdi(tolyl carbonate, etc., di(naphthyl)carbonate,di(chloronaphthyl)carbonate, phenyltolyl carbonate, chloronaphthylchlorophenyl carbonate, and the like. The haloformates suitable for useherein include bishaloformates of dihydric phenols such asbischloroformates of hydroquinone, etc. or glycols such asbis-haloformates of ethylene glycol, neopentyl glycol, polyethyleneglycol, etc. While other carbonate precursors will occur to thoseskilled in the art, carbonyl chloride, also known as phosgene ispreferred.

The preparation of copolyestercarbonates which may be employed in thecompositions of the present invention is described in U.S. Pat. Nos.3,030,331; 3,169,121; 3,207,814; 4,194,038 and 4,156,069.

The copolyestercarbonates which are preferred in the practice of thepresent invention include the aromatic polyestercarbonates derived fromdihydric phenols, aromatic dicarboxylic acids or their reactive esterforming derivatives such as the aromatic diacid halides, and phosgene. Aparticularly useful class of aromatic copolyestercarbonates is thatderived from bisphenol-A, isophthalic acid, terephthalic acid, or amixture of isophthalic acid and terephthalic acid, or the reactivederivatives of these acids such as terephthaloyl dichloride,isophthaloyl dichloride, or a mixture of isophthaloyl dichloride andterephthaloyl dichloride, and phosgene. The molar proportion of esterunits in the copolyestercarbonate is generally from about 25 to 90 molepercent and preferably about 35 to 80 mole percent. The molar range ofterephthalate units, the remainder of the copolymer ester unitspreferably comprising isophthalate units is generally from about 2 to 90percent, and preferably from about 5 to about 25 percent.

The aromatic carbonate polymers are commonly mixed with a second polymerand so on to produce blends having varying physical properties andutility. Generally, the polycarbonate content of such blends can rangebetween 1 to 99 parts by weight to correspondingly 99 to 1 parts byweight, based on 100 weight parts, of aromatic carbonate polymer tosecond polymer, etc.

Commonly, polyesters are a second polymer. Suitable polyesters may bederived from an aliphatic, aliphatic ether, or cycloaliphatic diol,containing from 2 to about 10 carbon atoms and one or more aromatic orcycloaliphatic dicarboxylic acids.

One preferred polyester is derived from an aliphatic diol and anaromatic dicarboxylic acid. Specific among these are the poly(alkyleneterephthalates, i.e. poly(ethylene terephthalate) and poly(butyleneterephthalate).

A variation of this first polyester replaces a portion of the aliphaticdiol and aromatic dicarboxylic acid with additional amounts of diolsand/or diacids in amounts of from 0.5 to 50 weight percent based on thetotal composition. The additional diacids can be aliphatic orcycloaliphatic with the number of carbon atoms ranging from 2 to 20.Likewise, additional diols can be cycloaliphatic or aliphatic with thenumber of carbon atoms covering the same range. Polyalkylene etherglycols can also be used where the alkylene portion has from 2 to 10carbon atoms and the entire glycol portion varies in molecular weightfrom 100 to 10,000. All such polyesters can be made following theteachings of, for example, U.S. Pat. Nos. 2,465,319 and 3,047,539.

A second preferred polyester is derived from a cycloaliphatic diol andan aromatic or cycloaliphatic dicarboxylic acid. These polyesters may beprepared, for example, by condensing either the cis- or transisomer (ormixtures thereof) of, for example, 1,4-cyclohexanedimethanol with adicarboxylic acid such as isophthalic and/or terephthalic acid. Examplesof additional aromatic dicarboxylic acids are1,2-di(p-carboxyphenyl)ethane, 4,4'-dicarboxydiphenyl ether, etc., andmixtures of these. Dicarboxylic acids containing fused rings can also bepresent, such as in 1,4- or 1,5-naphthalenedicarboxylic acids. Alsocontemplated are cycloaliphatic diacids, such as cyclohexanedicarboxylic acid. However, the preferred dicarboxylic acids areterephthalic acid or a mixture of terephthalic and isophthalic acids.

Still a third polyester is a copolyester derived from a cyclohexanedimethanol, an alkylene glycol and an aromatic dicarboxylic acid. Thesecopolyesters are prepared by condensing either the cis- or trans-isomer(or mixtures thereof) of, for example, 1,4-cyclohexanedimethanol and analkylene glycol with an aromatic or cycloaliphatic dicarboxylic acid. Apreferred such polyester may be derived from the reaction of either thecis- or trans-isomer (or mixtures thereof) of 1,4-cyclohexanedimethanoland ethylene glycol with terephthalic acid in a molar ratio of, forexample, 80:20: 100.

The polyesters employed in the practice of the invention will usuallyhave an intrinsic viscosity of from about 0.4 to about 2.0 dl/g., asmeasured in a 60:40 phenol:tetrachloroethane mixture, or similar solventat 23°-30° C. Such polyesters may be prepared according to U.S. Pat. No.2,901,466.

The aromatic carbonate polymers may be blended with other polymers aswell. Illustrative of these polymer types include acrylates,polyolefins, EDPM type polymers, styrenics, butadiene,poly(phenylene-ether), poly(ether-imide), polysulfone, polyarylates, andthe like.

Various other additives may be employed in their appropriate quantitiesif they do not substantially detract from the final application. Forexample, the composition can be thermally stabilized by a phosphite,hydrolytically stabilized by an epoxide, reinforced with glass fiber,flame retarded with a salt or brominated polymer, or colorants.

Ester compounds useful as stabilizers herein have functional groupsrepresented by (--COOR³) wherein R³ may be a substituted orunsubstituted, aromatic or aliphatic, hydrocarbon and the parent carboxycompound may likewise be substituted or unsubstituted, aromatic oraliphatic, and/or mono- or polyfunctional. Esters which have provenuseful include tetrakis(methylene[3,5-di-t-butyl-4-hydroxy-hydrocinnamate])methane, 2,2'oxamidobis(ethyl-3-(3,5-di-t-butyl-4-hydroxy-phenyl) propionate, and GOOD-RITE3125, herein designated a trifunctional hindered phenolic ester compound(see Example 107 for description of structure). Additional esters may beimagined by those skilled in the art.

Suitable alcohol (--OH) stabilizer compounds for use herein may beselected from mono, di-, or polyfunctional hydroxy compounds. Usually,the alcohol will contain from 2 to 50 carbon atoms and can be astraight, branched, cyclic and/or aromatic chain.

Diols and polyols are preferred. By way of illustration, such diolsinclude aliphatic diols, for example, ethylene glycol, propylene glycol,1,3-propanediol, 1,2-butanediol, 1,4-butanediol, meso-2,3-butanediol,1,2-pentanediol, 2,3-pentanediol, 1,4-pentanediol, 1,4-hexanediol, andthe like; alicyclic diols, for example, 1,2-cyclopentanediol,1,2-cyclohexanediol, and the like; branched acyclic diols, for example,2,3-dimethyl-2,3-butanediol (pinacol), and the like. Also useful withthis method are highly branched polyols as well as alkoxy substitutedcyclic or acyclic alkanes. Preferred diols are those in which at leastone of the hydroxy functionalities is a tertiary hydroxy, for example,2,5-dimethyl-2,5-hexanediol and 2-methyl-2,4-pentanediol.

A second preferred class of alcohols is the alkenols. These alcohols mayhave multiple points of unsaturation with hydroxy substitution occurringon either a saturated or unsaturated carbon. Effective alkenols include4-methyl-4-penten-2-ol, 3-methyl-penten-3-ol, 2-methyl-4-penten-2-ol,2,4-dimethyl-4-penten-2-ol, 2-phenyl-4-penten-2-ol, and 9-decen-1-ol.

A third preferred class of alcohols is the tertiary alcohols whichcontain at least one hydroxy substituted tertiary carbon. Specific suchcompounds include aliphatic tertiary carbons, such as,2-methyl-2,4-pentanediol, 2-phenyl-2-propanol,3-hydroxy-3-methyl-2-butanone, 2-phenyl-2-butanol, etc., andcycloaliphatic tertiary carbons, such as, 1-hydroxy-1-methylcyclohexane.

A fourth preferred class of alcohols is hydroxy methyl aromatics whichare intended to encompass compounds having hydroxy substitution on asaturated carbon attached to an unsaturated carbon in an aromatic ring.Preferably, the aromatic ring is benzene or naphthalene or, of course, asubstituted aromatic ring. The hydroxy substituted saturated carbon maybe a simple methylol group (--CH₂ OH) or it may be a member of a morecomplex hydrocarbon group, such as would be the case with (--CR⁴ HOH) or(--CR₂ ⁴ OH) wherein R⁴ is a complex or simple hydrocarbon. Thus,specific hydroxy methyl aromatics may be benzhydrol,1,3-benzenedimethanol, benzyl alcohol, 4-benzyl oxybenzyl alcohol, andbenzyl benzyl alcohol. The preferred conjugated hydroxy contains abenzylic alcohol group.

Thio (>S) compounds suitable for use herein are thiols, thioethers andcyclic thioethers. For example, thiols include 2-mercaptobenzothiazole,etc.; thioethers include dilaurylthiopropionate, etc. and cyclicthioethers include 1,4-dithiane, 1,4,8,11-tetrathiocyclotetradecane,etc. Preferred are the cyclic thioethers, especially cyclic thioetherscontaining more than one thioether group. A particularly preferredcyclic thioether contains a single intervening carbon between twothioether groups, for example, 1,3-dithiane. Of course, the cyclic ringmay contain oxygen or nitrogen members.

Diketone (>CO) compounds useful herein contain two carbonylfunctionalities, preferably separated by a single intervening carbonatoms. Suitable diketones include 2,4-pentadione, etc.

Sulfone (--SO₂) compounds suitable for use herein are of the generalformula

    R.sup.5 --SO.sub.2 --R.sup.6

wherein R⁵⁻⁶ may be the same or different and selected from the groupalkyl, aryl, alkoxy, aryloxy, etc. and substituted derivatives thereof.At least one of the R groups should be a substituted or unsubstitutedbenzyl. Specific sulfones suitable for use herein include benzylsulfone.

Suitable alkenes for use herein include alkenes represented by thegeneral formula ##STR6## wherein R⁷⁻¹⁰ may be the same or different andmay be selected from hydrogen, alkyl, cycloalkyl, alkenyl, cycloalkenyl,aryl, aralkyl, alkaryl, alkoxy, aryloxy and substituted derivativesthereof. A first preferred alkene as shown above is one in which R⁷⁻⁸are independently selected from alkyl, cycloalkyl, alkenyl,cycloalkenyl, aryl, aralkyl, alkaryl, and substituted derivativesthereof. Especially preferred such alkenes are

ones in which R⁷ is selected from the group consisting of aryl, aralkyl,and substituted derivatives thereof. A second preferred alkene as shownabove is one wherein at least one of R⁷ and R⁸ and at least one of R⁹and R¹⁰ are aryl or aralkyl such as, for example, 1,2-diphenyl ethene. Athird preferred alkene is one wherein at least one of R⁷⁻¹⁰ is metharyl,such as for example, allyl phenol. Of course, the R⁷⁻¹⁰ groups can belinked to form cyclic compounds. Useful alkenes are2,4-dimethyl-1-pentene, limonene, 2-phenyl-2-pentene,2,4-dimethyl-1-pentene, 1,4-diphenyl-1,3-butadiene, 2-methyl-1-undecene,1-dodecene.

Suitable hydroaromatic compounds are the partially hydrogenated carbonskeletons of an aromatic system or an aromatic system in combinationwith an unsaturated ring. Preferred aromatic systems are benzene ornaphthalene based systems. Examples of suitable hydroaromatic compoundsare indane, 5,6,7,8-tetrahydro-1-naphthol,5,6,7,8-tetrahydro-2-naphthol, 9,10-dihydro anthracene,9,10-dihydrophenanthrene, 1-phenyl-1-cyclohexane,1,2,3,4-tetrahydro-1-naphthol, and others.

Suitable pyran compounds include hydrogenated and nonhydrogenated,substituted and unsubstituted pyran. Substituent groups may be chosenfrom alkyl, aryl, alkoxy, aryloxy, etc., and may be positioned on anycarbon of the pyran ring. Preferably, the substituent group is alkoxy oraryloxy and located on the six position. It is also preferred that thepyran compound be hydrogenated. Representative of the diethers for useherein are dihydropyranyl ethers and tetrahydropyranyl ethers.

Additional compounds which function as stabilizers in the presentprocess are high molecular weight oxamide phenolics, for example,2,2-oxamido bis-[ethyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate],high molecular weight oxalic anilides and their derivatives, and aminessuch as thiourea.

Suitable stabilizing compounds may be a member of more than one of theabove described groups. In other words, a single compound may have 2 ormore functionalities characteristic of the groups as described above. Ofcourse, each such compound whether having 1, 2, or more functionalitieswill vary in stabilizing effectiveness and thus, depending on thestabilizing compound chosen, the effective amount of such compound willalso change. Generally, it is not desirable to choose a compound thatwould require more than 5 weight parts per 100 parts by weight resin toachieve the desired degree of stabilization. Ideally, the stabilizingcompound should be added in an amount between about 0.01 weight partsand 0.50 weight parts per 100 weight parts resin. Mixtures ofstabilizing compounds may also be used.

The admixtures of the aromatic carbonate polymer and stabilizingcompound are simply prepared by standard techniques, for example, bysimple blending or dry mixing and melt extruding at an elevatedtemperature. The extruded admixture is then molded into a piece ofspecific dimensions or further extruded into a film or sheet product.

The radiation employed to achieve sterilization of the particular objectis ionizing radiation, usually gamma radiation produced from a cobalt-60or cesium-137 radioactive nuclei. The quantity of gamma radiationrequired for sterilization is generally 0.5 to about 7 Megarads.Preferably, the irradiation is from about 1.0 to 3.0 Megarads. A secondtype of radiation, electron beam radiation, is also suitable forsterilization. Electron beam radiation is produced in a high voltageelectron acceleration.

DESCRIPTION OF SPECIFIC EMBODIMENTS

Further illustration of this invention is set forth in the followingexamples. There is no intention to limit the scope of the invention tomerely what is shown.

The following resins were used in the formulations of the examples:

Polycarbonate--LEXAN® 145 resin, poly(bisphenol-A carbonate), GeneralElectric Company (contains 0.06% by weight of a conventional phosphitestabilizer).

Poly(ester-carbonate)--an ester content of 75% mole % and being 93 mole% isophthalate and 7 mole % terephthalate.

Polycarbonate/polyester blend--80 weight parts polycarbonate with 20weight parts KODAR A150 resin, Eastman Kodak Company,poly(1,4-cyclohexanedimethanolterephthalate-co-isophthalate) and aphosphorous acid stabilizer.

Unless otherwise noted, the formulations containing 100 weight parts ofthe indicated resin or blend were extruded on a sterling single screw(13/4) extruder at a melt temperature of T1. Test plaques 1/8" inthickness were injection molded on a 3 oz. Van Dorn using a T2 melt settemperature, a T3 mold cavity temperature, and a 10/20 cycle time. T1,T2, and T3 were set according to the resin or blend used:

    ______________________________________                                        Polycarbonate --   Tl = 260° C.                                                           T2 = 302° C.                                                           T3 =  82° C.                                        Poly(ester-carbonate) --                                                                         Tl = 299° C.                                                           T2 = 343° C.                                                           T3 = 116° C.                                        Polycarbonate/Polyester --                                                                       Tl = 282° C.                                                           T2 = 282° C.                                                           T3 =  66° C.                                        ______________________________________                                    

The samples were irradiated by one of the following methods:

Gamma Irradiation--samples were exposed to a Co⁶⁰ source on a continuousconveyor system, dosimetry was monitored with a calibrated NBS,radiochromic, nylon dosimeter and different Co⁶⁰ sources were used.

Electron Beam Irradiation--samples irradiated on one side in air using alinear cathode electron beam system, 5 Mrad dose, 20 ft/min line speed,5 mA beam current, 200 KV terminal voltage, dosimetry monitored with acalibrated NBS, radiochromic, nylon dosimeter.

Unless otherwise noted, testing of the samples has been conducted withgamma radiation and yellowness index, Y.I., measured on a Gardnercolorimeter in accordance with ASTM D1925 both before and afterradiation. The less change in Y.I. upon irradiation, the more effectivethe stabilizer.

    __________________________________________________________________________                   AMOUNT, phr                                                                              Y.I.  Y.I.   Y.I.   Y.I.                            EXAMPLE                                                                              ADDITIVE                                                                              POLYCARBONATE                                                                            (0 MRAD)                                                                            (1.5 MRAD)                                                                           (2.7 MRAD)                                                                           (5.8 MRAD)                      __________________________________________________________________________    C      None    --         2.4   9.7    16.7   31.5                            1      Pentaery-                                                                             0.32       2.5   12.7   15.6   31.6                                   thritol                                                                2      Triphenyl-                                                                            0.20       18.0  18.6   23.8   37.7                                   methanol                                                               3      Neopentyl                                                                             0.08       2.2   9.7    14.3   31.1                                   alcohol                                                                4      2,2-dimethyl-                                                                         0.09       2.1   9.6    13.7   31.9                                   1,3-propanediol                                                        5      Mannitol                                                                              0.16       3.3   10.4   13.2   28.3                            C      None    --         2.4   10.7   17.8   36.2                            6      1,4-butane-                                                                           0.08       2.3   9.6    15.5   27.6                                   diol                                                                   7      1,4-butane-                                                                           0.16       2.1   10.2   15.4   26.8                                   diol                                                                   8      Octadecanol                                                                           0.23       2.1   9.6    16.8   33.4                            9      Octadecanol                                                                           0.46       2.0   9.4    16.4   33.5                            10     Cyclohexane-                                                                          0.01       2.4   9.5    16.3   32.2                                   diol                                                                   11     Cyclooctane-                                                                          0.12       2.3   9.2    16.6   30.5                                   diol                                                                   12     Cyclodecanol                                                                          0.16       2.1   10.0   18.8   35.4                            __________________________________________________________________________

    __________________________________________________________________________                   AMOUNT, phr                                                                              Y.I.  Y.I.     Y.I. -EXAMPLE ADDITIVE POLYCARBON                                             ATE (0 MRAD) (2.6/2.7 MRAD) (5.4                                              MRAD)                                __________________________________________________________________________    C      None    --         1.9   19.2     42.5                                 13     2,4-pentane                                                                           0.09       1.6   14.8     38.3                                        diol                                                                   14     2,4-pentane                                                                           0.09       1.8   16.9     37.3                                        dione                                                                  15     2,5-dimethyl-                                                                         0.12       1.7   14.5     29.1                                        2,5-hexanediol                                                         16     2-methyl-                                                                             0.10       1.6   11.4     29.0                                        2,4-pentane-                                                                  diol                                                                   17     2-methyl-                                                                             0.15       2.0   10.6     25.3                                        2,4-pentane-                                                                  diol                                                                    18*   2-methyl-                                                                             0.10       1.6   10.8     24.0                                        2,4-pentane-                                                                  diol                                                                   19     Cyclohexane-                                                                          0.12       1.6   16.9     42.5                                        dimethanol                                                             __________________________________________________________________________     *Containes also 0.31 phr tri(hexylene glycol)biborate                    

    __________________________________________________________________________                  AMOUNT, phr                                                                              Y.I.  Y.I.   Y.I. -EXAMPLE ADDITIVE POLYCARBONATE                                           (0 MRAD) (3.0 MRAD) (5.5               __________________________________________________________________________                                          MRAD)                                   C      None   --         2.2   21.6   40.3                                    20     2-methyl-                                                                            0.1        1.9   11.8   26.4                                           2,4-pentane-                                                                  diol                                                                   21     2-methyl-                                                                            0.09       2.1   15.2   24.9                                           2-pentanol                                                             22     2-phenyl-2-                                                                          0.12       2.0   18.6   33.9                                           propanol                                                               23     2-phenyl-2-                                                                          0.13       2.0   15.1   25.7                                           butanol                                                                24     1,3-butane-                                                                          0.08       1.9   16.3   32.7                                           diol                                                                   __________________________________________________________________________

    __________________________________________________________________________                     AMOUNT, phr                                                                              Y.I.  Y.I.     Y.I. -EXAMPLE ADDITIVE POLYCARB                                               ONATE (0 MRAD) (2.6/2.7                                                       MRAD) (5.1/5.6                     __________________________________________________________________________                                               MRAD)                              C      None      --         1.9   21.9     42.4                               25     2,3-dimethyl-2,3-                                                                       0.10       1.8   19.9     40.0                                      butanediol                                                             26     3-hydroxy-3-methyl-                                                                     0.09       1.9   20.2     34.7                                      2-butanone                                                             27     4-hydroxy-4-methyl-                                                                     0.10       1.9   18.9     34.5                                      2-pentanone                                                            28     2-methyl-2,4-                                                                           0.04       1.6   15.3     30.2                                      pentanediol                                                            29     2-methyl-2,4-                                                                           0.10       1.6   10.9     20.5                                      pentanediol                                                            30     2-methyl-2,4-                                                                           0.40       1.5   10.6     17.3                                      pentanediol                                                            __________________________________________________________________________

    __________________________________________________________________________                      AMOUNT, phr                                                                              Y.I.  Y.I.   Y.I. -EXAMPLE ADDITIVE POLYCARBO                                              NATE (0 MRAD) (3.0 MRAD) (6.1                                                 MRAD)                               __________________________________________________________________________    C      None       --         1.9   22.1   55.2                                31     2-methyl,2,4-pentane-                                                                    0.10       1.6   11.5   37.3                                       diol                                                                   32     3-ethyl-3-pentanol                                                                       0.10       2.2   19.8   45.5                                33     3-ethyl-3-heptanol                                                                       0.12       1.5   20.7   47.6                                34     3-ethyl-3-heptanol                                                                       0.25       1.5   18.6   40.1                                35     4-methyl-4-nonanol                                                                       0.13       1.6   19.0   42.4                                36     2,7-dimethyl-2,7-                                                                        0.15       1.6   20.1   44.3                                       octanediol                                                             C      None       --         1.8   25.0   49.1                                37     2,4-dimethyl-2,4-                                                                        0.11       1.7   14.1   28.9                                       pentanediol                                                            38     2-methyl-2,4-pentane-                                                                    0.10       1.5   11.3   30.1                                       diol                                                                   __________________________________________________________________________

    __________________________________________________________________________                     ADDITIVE, phr                                                                            Y.I.  Y.I.                                        EXAMPLE                                                                              ADDITIVE  POLYCARBONATE                                                                            (0 MRAD)                                                                            (5 MRAD)*                                   __________________________________________________________________________    C      None      --         1.5   4.3                                         39     2-methyl-2,4-                                                                           0.10       1.6   2.8                                                pentanediol                                                            40     2,4-pentanediol                                                                         0.09       1.6   3.4                                         41     2-methyl-2-pentanol                                                                     0.09       1.7   3.7                                         C      None      --         1.9   4.5                                         42     2,5-dimethyl-3,5-                                                                       0.12       2.3   4.1                                                hexanediol                                                                              0.12       2.3   4.1                                         C      None      --         1.7   4.5                                         43     2-methyl-2,4-                                                                           0.04       1.6   3.6                                                pentanediol                                                            44     2-methyl-2,4-                                                                           0.10       1.6   3.2                                                pentanediol                                                            45     2-methyl-2,4-                                                                           0.40       1.5   2.7                                                pentanediol                                                            __________________________________________________________________________     *Electron beam irradiation                                               

    __________________________________________________________________________                  ADDITIVE, phr                                                                 PLYCARBONATE/                                                                             Y.I   Y.I.     Y.I.                                 EXAMPLE                                                                              ADDITIVE                                                                             POLYESTER*  (0 MRAD)                                                                            (2.6/2.7 MRAD)                                                                         (5.3/5.4 MRAD)                       __________________________________________________________________________    C      None   --          -13.6 1.1      17.4                                 46     2-methyl-2,4-                                                                        0.10        -12.9 -2.0     11.9                                        pentanediol                                                            __________________________________________________________________________     *80/20 weight ratio polycarbonate/polyester and a violet dye             

    __________________________________________________________________________                  ADDITIVE, phr   Y.I.  Y.I.                                      EXAMPLE                                                                              ADDITIVE                                                                             POLY(ESTERCARBONATE)                                                                          (0 MRAD)                                                                            (2.9/3.0 MRAD)                            __________________________________________________________________________    C      NONE   --              6.5   17.2                                      47     2-methyl-2,4-                                                                        0.08            6.1   12.4                                             pentanediol                                                            48     2-methyl-2,4-                                                                        0.12            5.6   11.9                                             pentanediol                                                            __________________________________________________________________________

    __________________________________________________________________________                  ADDITIVE, phr   Y.I.  Y.I.                                      EXAMPLE                                                                              ADDITIVE                                                                             POLY(ESTERCARBONATE)                                                                          (0 MRAD)                                                                            (5.0 MRAD)*                               __________________________________________________________________________    C      None   --              6.0   7.5                                       49     2-methyl-2,4-                                                                        0.12            5.1   6.1                                              pentanediol                                                            __________________________________________________________________________     *Electron beam irradiation                                               

    __________________________________________________________________________                   ADDITIVE, phr                                                                            Y.I.  Y.I.     Y.I.                                 EXAMPLE                                                                              ADDITIVE                                                                              POLYCARBONATE                                                                            (0 MRAD)                                                                            (2.6/3.0 MRAD)                                                                         (5.5/4.9 MRAD)                       __________________________________________________________________________    C      None    --         2.3   24.3     45.3                                 50     Benzyl ether                                                                          0.17       2.2   21.7     37.6                                 51     4-benzyl-oxy-                                                                         0.18       2.6   14.6     23.2                                        benzyl alcohol                                                         52     benzyl-benzyl                                                                         0.17       2.4   17.7     31.3                                        alcohol 0.17       2.4   17.7     31.3                                 53     Benzyl alcohol                                                                        0.09       2.0   12.6     18.8                                 __________________________________________________________________________

    __________________________________________________________________________                  ADDITIVE, phr                                                                            Y.I.  Y.I.   Y.I.                                    EXAMPLE                                                                              ADDITIVE                                                                             POLYCARBONATE                                                                            (0 MRAD)                                                                            (3.1 MRAD)                                                                           (5.5/5.7 MRAD)                          __________________________________________________________________________    C      None   --         2.0   20.3   42.4                                    54     Benzhydrol                                                                           0.16       1.9   14.3   24.3                                    __________________________________________________________________________

    __________________________________________________________________________                   ADDITIVE, phr                                                                            Y.I.  Y.I.     Y.I.                                 EXAMPLE                                                                              ADDITIVE                                                                              POLYCARBONATE                                                                            (0 MRAD)                                                                            (3.3/3.2 MRAD)                                                                         (5.1/5.0 MRAD)                       __________________________________________________________________________    C      None    --         1.9   26.7     37.4                                 55     1,2-dimethanol                                                                        0.12       3.3   22.6     26.9                                        benzene                                                                56     1,3-dimethanol                                                                        0.12       1.7   13.2     15.5                                        benzene                                                                57     1,4-dimethanol                                                                        0.12       1.6   12.9     15.1                                        benzene                                                                __________________________________________________________________________

    __________________________________________________________________________                       ADDITIVE, phr                                                                            Y.I.  Y.I.                                      EXAMPLE                                                                              ADDITIVE    POLYCARBONATE                                                                            (0 MRAD)                                                                            (5.0/5.2 MRAD)                            __________________________________________________________________________    C      None        --         2.1   44.0                                      58     1,3-dimethanol benzene                                                                    0.12       1.9   18.6                                      59     1,3-dimethanol benzene/                                                                   1.12/0.10  1.8   16.5                                             2-methyl-2,4-pentandiol                                                __________________________________________________________________________

    __________________________________________________________________________                   ADDITIVE, phr                                                                            Y.I.  Y.I.     Y.I.                                 EXAMPLE                                                                              ADDITIVE                                                                              POLYCARBONATE                                                                            (0 MRAD)                                                                            (3.3/3.2 MRAD)                                                                         (5.1/5.0 MRAD)                       __________________________________________________________________________    C      None    --         2.1   25.1     37.3                                 60     Benzyl sulfone                                                                        0.24       2.3   25.5     23.7                                 __________________________________________________________________________

    __________________________________________________________________________                   ADDITIVE, phr                                                                            Y.I.  Y.I.  Y.I.                                    EXAMPLE                                                                              ADDITIVE                                                                              POLYCARBONATE                                                                            (0 MRAD)                                                                            (3 MRAD)                                                                            (6.1 MRAD)                              __________________________________________________________________________    C      None    --         2.7   22.6  49.5                                    61     Benzyl alcohol                                                                        0.04       1.9   13.7  24.3                                    62     Benzyl alcohol                                                                        0.12       1.5   11.5  18.4                                    63     Benzyl alcohol                                                                        0.20       1.6   10.7  16.3                                    64     Benzyl alcohol                                                                        0.50       2.0    9.8  13.3                                    65     Benzyl alcohol                                                                        1.0        7.7    9.7  11.5                                    __________________________________________________________________________

    __________________________________________________________________________                      ADDITIVE, phr                                                                            Y.I.  Y.I.                                       EXAMPLE                                                                              ADDITIVE   POLYCARBONATE                                                                            (0 MRAD)                                                                            (5 MRAD)*                                  __________________________________________________________________________    C      None       --         1.9   4.5                                        66     Benhydrol  0.16       1.9   3.3                                        C      None       --         1.9   4.7                                        67     Benzenedimethanol                                                                        0.12       1.7   3.0                                        C      None       --         1.8   4.8                                        68     1,3-benzenedimethanol                                                                    0.12       1.7   3.1                                        69     Benzyl alcohol                                                                           0.10       1.7   3.1                                        70     Benzyl alcohol                                                                           0.19       1.7   3.0                                        __________________________________________________________________________     *Electron beam irradiation                                               

    __________________________________________________________________________                   ADDITIVE, phr                                                                 POLYCARBONATE/                                                                            Y.I.  Y.I.     Y.I.                                EXAMPLE                                                                              ADDITIVE                                                                              POLYESTER*  (0 MRAD)                                                                            (2.5/2.8 MRAD)                                                                         (4.9/5.1 MRAD)                      __________________________________________________________________________    C      None    --          3.1   9.5      15.1                                71     Benzyl alcohol                                                                        0.09        5.2   9.5      12.1                                __________________________________________________________________________     *80/20 weight ratio polycarbonate/polyester                              

    __________________________________________________________________________                   ADDITIVE, phr                                                                 POLY(ESTER-                                                                            Y.I.  Y.I.     Y.I.                                   EXAMPLE                                                                              ADDITIVE                                                                              CARBONATE                                                                              (0 MRAD)                                                                            (2.5/2.8 MRAD)                                                                         (4.9/5.1 MRAD)                         __________________________________________________________________________    C      None    --       4.9   15.1     21.6                                   72     Benzyl alcohol                                                                        0.09     5.0   12.7     17.0                                   73     Benzyl alcohol                                                                        0.19     6.6   13.9     18.1                                   __________________________________________________________________________

    __________________________________________________________________________                    ADDITIVE, phr                                                                            Y.I.  Y.I.     Y.I.                                EXAMPLE                                                                              ADDITIVE POLYCARBONATE                                                                            (0 MRAD)                                                                            (3.3/3.2 MRAD)                                                                         (5.1/5.0 MRAD)                      __________________________________________________________________________    C      None     --         2.1   25.1     37.3                                74     1,2,3,4-tetrahydro-                                                                    0.13       2.3   11.6     14.3                                       1-naphthol                                                             75     1,2,3,4-tetrahydro-                                                                    0.13       2.1   19.6     21.7                                       naphthalene                                                            __________________________________________________________________________

    __________________________________________________________________________                      ADDITIVE, phr                                                                            Y.I.  Y.I.                                       EXAMPLE                                                                              ADDITIVE   POLYCARBONATE                                                                            (0 MRAD)                                                                            (5 MRAD)*                                  __________________________________________________________________________    C      None       --         2.0   4.7                                        76     1,2,3,4-tetrahydro-                                                                      0.13       2.3   2.0                                               1-naphthol                                                             77     1,2,3,4-tetrahydro-                                                                      0.11       3.6   4.0                                               naphthalene                                                            C      None       --         2.4   5.1                                        78     1-phenyl-cyclohexane                                                                     0.13       2.3   3.6                                        79     5,6,7,8-tetrahydro-2-                                                                    0.13       3.3   4.7                                               naphthol                                                               80     9,10-dihydroanth-                                                                        0.15       2.1   3.9                                               racene                                                                 __________________________________________________________________________     *Electron beam irradiation                                               

    __________________________________________________________________________                    ADDITIVE, phr                                                                 POLY(ESTER                                                                             Y.I.  Y.I.     Y.I.                                  EXAMPLE                                                                              ADDITIVE CARBONATE)                                                                             (0 MRAD)                                                                            (2.5/2.8 MRAD)                                                                         (4.9/5.1 MRAD)                        __________________________________________________________________________    C      None     --       6.6   16.8     20.9                                  81     5,6,7,8-tetra-                                                                         0.15     5.4   14.9     18.9                                         hydro-1-naphthol                                                       __________________________________________________________________________

    __________________________________________________________________________                   ADDITIVE, phr                                                                            Y.I.  Y.I.   Y.I.                                   EXAMPLE                                                                              ADDITIVE                                                                              POLYCARBONATE                                                                            (0 MRAD)                                                                            (3.1 MRAD)                                                                           (5.5/5.7 MRAD)                         __________________________________________________________________________    C      None    --         2.0   20.3   42.0                                   82     1,3-dithiane                                                                          0.10       2.4   10.3   19.9                                   83     1,4-dithiane                                                                          0.10       2.1   14.9   32.2                                   84     2,5-diol-1,4-                                                                         0.13       46.7  42.8   45.4                                          dithiane                                                               85     1,4,8,11-tetra-                                                                       0.23       2.4   13.1   27.6                                          thiocyclo-tetra-                                                              decane                                                                 86     Sulfur  0.22       70.8  67.6   70.3                                   __________________________________________________________________________

    __________________________________________________________________________                    ADDITIVE, phr                                                                            Y.I.  Y.I.                                         EXAMPLE                                                                              ADDITIVE POLYCARBONATE                                                                            (0 MRAD)                                                                            (5 MRAD)*                                    __________________________________________________________________________    C      None     --         1.9   4.5                                          87     1,3-dithiane                                                                           0.10       2.2   3.3                                          88     1,4,8,11-tetrathio-                                                                    0.20       2.4   4.1                                                 cyclotetradecane                                                       __________________________________________________________________________     *Electron beam irradiation                                               

    __________________________________________________________________________                     ADDITIVE, phr                                                                            Y.I.  Y.I.   Y.I.                                 EXAMPLE                                                                              ADDITIVE  POLYCARBONATE                                                                            (0 MRAD)                                                                            (3.0 MRAD)                                                                           (6.1 MRAD)                           __________________________________________________________________________    C      None      --         1.8   25.0   49.1                                 89     2,4-dimethyl-1-                                                                         0.08       1.7   21.7   42.1                                        pentene                                                                90     2,4,-dimethyl-1-                                                                        0.13       1.7   21.3   43.0                                        pentene                                                                91     4-methyl-4-                                                                             0.09       1.6   11.2   26.9                                        pentene-2-ol                                                           92     4-methyl-4-                                                                             0.13       1.5   10.3   17.4                                        pentene-2-ol                                                           93     2-methyl-2-                                                                             0.09       1.7   14.1   34.8                                        pentene-2-ol                                                           94     2-methyl-4-                                                                             0.13       1.5   14.2   34.7                                        pentene-2-ol                                                           95     2,4-dimethyl-4-                                                                         0.10       1.6   15.4   33.9                                        pentene-2-ol                                                           96     2-phenyl-4-                                                                             0.14       1.7   15.9   31.5                                        pentene-2-ol                                                           97     2-phenyl-2-pentene                                                                      0.13       1.6   12.5   21.2                                 __________________________________________________________________________

    __________________________________________________________________________                    ADDITIVE, phr                                                                            Y.I.  Y.I.     Y.I.                                EXAMPLE                                                                              ADDITIVE POLYCARBONATE                                                                            (0 MRAD)                                                                            (2.6/3.0 MRAD)                                                                         (4.9/5.5 MRAD)                      __________________________________________________________________________    C      None     --         2.5   27.5     42.1                                106    3,4-dihydro-2-                                                                         0.10       4.0   12.5     17.2                                       ethoxy-2H-pyran                                                        __________________________________________________________________________

    __________________________________________________________________________                    ADDITIVE, phr                                                                            Y.I.  Y.I.                                         EXAMPLE                                                                              ADDITIVE POLYCARBONATE                                                                            (0 MRAD)                                                                            (5 MRAD)*                                    __________________________________________________________________________    C      None     --         1.9   4.7                                          98     3-methyl-pentene-                                                                      0.09       1.6   3.2                                                 3-ol                                                                   __________________________________________________________________________     *Electron beam irradiation                                               

    __________________________________________________________________________                        ADDITIVE, phr                                                                            Y.I.  Y.I.                                     EXAMPLE                                                                              ADDITIVE     POLYCARBONATE                                                                            (0 MRAD)                                                                            (3.1/3.2 MRAD)                           __________________________________________________________________________    C      None         --         1.9   21.7                                      99    1,4-diphenyl-1,3-butadiene                                                                  .18       1.7   19.4                                     100    1-dodecene   0.15       1.6   18.3                                     101    trans-stilbene                                                                             0.15       2.4   16.7                                     102    2-methyl-undecene                                                                          0.15       1.7   18.6                                     103    Limonene     0.12       1.9   12.4                                     104    Allyl phenol 0.11       2.3   16.0                                     105    9-decen-l-ol 0.15       1.6   18.2                                     __________________________________________________________________________

    __________________________________________________________________________                      AMOUNT, phr   RADIATION                                     EXAMPLE                                                                              ADDITIVE   POLYCARBONATE                                                                            YI.sub.0                                                                         DOSE (MRAD)                                                                            YI.sub.final                         __________________________________________________________________________    C      None       --         2.7                                                                              5.0      35.2                                 107    Trifunctional                                                                            0.2        4.6                                                                              5.3      21.7                                        hindered phenolic                                                             ester.sup.a                                                            108    Dilaurylthio-                                                                            0.2        3.7                                                                              5.3      22.0                                        propionate.sup.b                                                       109    1,4-cyclohexane                                                                          0.2        3.2                                                                              5.3      22.9                                        dimethanol                                                             110    2,5-dimercapto-                                                                          0.2        28.6                                                                             5.0      35.9                                        1,3,4-thiadiazole.sup.c                                                111    Thiourea    0.05      10.1                                                                             5.0      21.9                                 112    2-mercapto 0.5        5.3                                                                              5.3      22.6                                        benzothiazole                                                          113    2,2-oxamido bis(ethyl                                                                    0.2        16.8                                                                             5.2      39.7                                        3-[3,5-di-tert-butyl-                                                         4-hydroxyphenyl])                                                             propionate.sup.e                                                       114    Oxalic anilide                                                                           0.2        3.1                                                                              5.0      23.0                                        derivative.sup.f                                                       115    Pentaerythritol                                                                          0.2        2.4                                                                              5.0      18.1                                 116    Trimethylol propane                                                                      0.2        3.1                                                                              5.0      26.2                                 117    Tetrakis(2,4-di-t-                                                                       0.1        2.0                                                                              5.0      24.0                                        butylphenyl)4,4'-                                                             biphenylenedi-                                                                phosphite.sup.g                                                        118    Tetrakis(methylene                                                                       0.1        2.5                                                                              2.5      16.1                                        [3,5-di-t-butyl-4-                                                            hydroxy-hydrocinna-                                                           mate])methane.sup.h                                                    __________________________________________________________________________

In the foregoing table, the letter designations refer to the followingcommercial materials:

a=GOOD-RITE® 3125, B.F. Goodrich Co.,3,5-ditert-butyl-4-hydroxyhydrocinnamic acid triester with 1,3,5-tris(2-hydroxy-ethyl)-s- tri-azine-2,4,6,(1H, 3H, 5H)-trione.

b=CYANOX® LTDP, American Cyanamid Co.

c=VANCHEM® DMTD, R.T. Vanderbilt Co., Inc.

e=NAUGARD® XL-1, Uniroyal Corp., an oxamide phenolic.

f=SANDUVOR® VSU, Sandoz Co.

g=SANDOSTAB P EPQ, Sandoz Co.

h=IRGANOX® 1010, Ciba-Geigy Corp., a high molecular weight stericallyhindered phenolic compound.

EXAMPLE 121

The following composition was extruded from 260° to 316° C. andinjection molded into test plaques 1/8" in thickness using a melttemperature of from 260° to 304° C. Measurement of yellowness index wasmade on a Pacific Scientific Spectrogard II unit in accordance with ASTMD-1925.

    ______________________________________                                               EXAMPLE       C         121                                            ______________________________________                                                 Polycarbonate   50        50                                                  Polyester       50        50                                         8V       Trifunctional   --        0.2                                                 hindred phenolic                                                              ester                                                                         Mixed red and   0.001     0.001                                               blue dyes                                                                     YI (0 Mrads)    --        --                                                  YI (5 Mrads)    7.5       4.1                                        ______________________________________                                    

    __________________________________________________________________________                     ADDITIVE, phr                                                                            Y.I.  Y.I.                                        EXAMPLE                                                                              ADDITIVE  POLYCARBONATE                                                                            (0 MRAD)                                                                            (5.0/5.2 MRAD)                              __________________________________________________________________________    C      None      --         5.1   42.4                                        122    2,2-oxamido bis                                                                         0.2        0.8** 24.5**                                             (ethyl-3-[3,5-di-                                                             t-butyl-4-hydroxy-                                                            phenyl])propionate*                                                    __________________________________________________________________________     *NAUGARD ® XL1 compound                                                   *Green color formed                                                      

    __________________________________________________________________________                  ADDITIVE, phr                                                                            Y.I.  Y.I.    Y.I.                                   EXAMPLE                                                                              ADDITIVE                                                                             POLYCARBONATE                                                                            (0 MRAD)                                                                            (2.6/3 MRAD)                                                                          (5.5/4.9 MRAD)                         __________________________________________________________________________    C      None   --         2.3   26.1    48.9                                   123    trifunctional                                                                        0.2        1.7   15.0*   34.9*                                         hindered phe-                                                                 nolic ester                                                            __________________________________________________________________________     *Green color formed                                                      

    __________________________________________________________________________                    ADDITIVE, phr                                                                            Y.I.  Y.I.   Y.I.   Y.I.                           EXAMPLE                                                                              ADDITIVE POLYCARBONATE                                                                            (0 MRAD)                                                                            (1.5 MRAD)                                                                           (2.8 MRAD)                                                                           (6.0 MRAD)                     __________________________________________________________________________    C      None     --         2.7   10.5   26.5   58.2                           124    dilaurylthio-                                                                          0.2        6.3   13.9   26.5   50.3                                  propionate*                                                            125    oxalic anilide                                                                         0.2        2.9   10.7   25.4   51.1                                  derivative**                                                           126    tetrakis(2,4-                                                                          0.2        3.4   11.9   27.6   54.5                                  di-t-butylphenyl)-                                                            4,4-biphenylene-                                                              diphosphite                                                            __________________________________________________________________________     *CYANOX ® LTDP compound                                                   **SANDUVOR ® VSU compound                                                 ***SANDOSTAB ® PEPQ compound                                         

What is claimed is:
 1. A method for sterilizing an aromatic carbonatepolymer, said method comprising:(i) imparting enhanced stability againststerilizing radiation to an aromatic carbonate polymer by admixing aneffective amount of a thiol compound effective therewith to inhibityellowing upon exposure to sterilizing radiation, said thiol beingselected from the group consisting of 2-mercaptobenzothiazol and2,5-dimercapto-1,3,4-thiadiazone, and (ii) exposing said aromaticcarbonate polymer to sterilizing radiation.